Protective grounding jumper cable tester and testing method

ABSTRACT

A protective grounding jumper cable tester basically includes a housing, a direct current power supply, a pair of jumper attachment terminals, a pair of test probe terminals, a current applying circuit connected between the direct current power supply and the pair of jumper attachment terminals for applying a direct current through a jumper cable attached between the jumper attachment terminals, and a resistance sensing circuit connected to the test probe terminals for sensing resistance to the flow of the direct current through the jumper cable by using a pair of test probes connected to the test probe terminals. A protective grounding jumper cable testing method includes connecting a jumper cable that is to be tested between a pair of terminals, applying a direct current to the cable, observing a current sensing meter while adjusting the direct current flowing through the jumper cable, either continuing with testing of the jumper cable if the direct current can be adjusted to a first preselected quantity, retest the jumper cable after inspecting and maintaining it or reject the jumper cable, setting a resistance sensing meter to sense resistance within a first preselected test range, contacting a pair of test probes to the terminals to indicate the resistance of the jumper cable to the direct current, comparing the resistance indicated by the resistance sensing meter with the first preselected test range, and, based on the comparison, either accept the jumper cable, retest the jumper cable after inspecting and maintaining it or reject the jumper cable.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to testing of grounding jumpercables and, more particularly, is concerned with a grounding jumpercable tester and testing method for determining if the resistance of agrounding jumper cable to current flow is below a predetermined safelevel.

2. Description of the Prior Art

During maintenance of a power line, it may become accidentally energizeddue to the inadvertent closing of a breaker or switch or due to mutualinduction from parallel live lines. To protect workers from electricshock should a fault occur, grounding jumper cables are installed invarious configurations to form a jumper system. Grounding jumper cablesare conductive cables that have attachment means, such as clamps, ateither end. The jumper system provides a path for current to flow aroundthe worker to a neutral line or to the earth. However, in order for thejumper system to adequately protect the worker, it must provide a verylow resistance path to current flow so that the voltage drop across theworker is within a safe level should a fault occur.

The maximum allowable resistance of the jumper system can be determinedbased upon assumptions concerning the available fault current at thework site, the duration of the available fault current, and the level ofsafety to be provided. Once the maximum allowable jumper systemresistance is determined, individual grounding jumper cables can beselected to form the jumper system. Since the resistance of the jumpersystem is determined primarily by the resistance of each of theindividual jumper cables, it is necessary to determine the resistance ofthe individual jumper cables. Additionally, since they may be damagedduring storage, transport or use, individual jumper cables should beperiodically tested to ensure that their resistance remains suitable forthe desired level of protection.

Grounding jumper cable tester devices exist, such as the onemanufactured by Hasting's Fiberglass Corporation, that are designed totest the resistance of a jumper cable to current flow. The devices testthe resistance of a jumper cable by relying on Ohm's law which definesthe mathematical relationship between voltage, current and resistance. Aknown current is applied through the cable and the voltage drop acrossthe cable is measured. With the current and voltage known, theresistance can be determined. However, the prior art jumper cabletesting device identified above utilizes a current transformer toprovide an alternating test current. This presents two significantdrawbacks.

The first drawback is the inductance associated with alternatingcurrent. When alternating current flows through the jumper cable,inductance can function similar to resistance and cause a voltage drop.Such an induced voltage drop may result in an inaccurately highresistance determination. The effect of inductance is particularly acuteif the cable is coiled or on a conductive surface. Thus, when using analternating test current, it is critical to take steps to ensure thatthe jumper cable is positioned properly to minimize the possible effectof inductance.

The second drawback is the low testing voltage. Many jumper cables havealuminum clamps. A thin aluminum oxide coating forms on the clamps. Thiscoating is highly resistant to current flow but easily breaks down whena sufficient voltage level, in the range of 5 to 10 volts, is applied.The voltage levels encountered at work sites are more than sufficient tobreak down any aluminum oxide coating on the clamps making theresistance of the coating irrelevant. However, if sufficient voltage isnot applied during testing, the thin aluminum oxide coating can raisethe resistance of the jumper cable and result in the unnecessaryrejection of the jumper cable. While the current transformer used in theprior known devices provides a sufficiently high alternating testcurrent, it does so at the expense of voltage. The voltage drop createdby prior alternating current jumper cable test devices is ofteninadequate to break down the aluminum oxide coating resulting in aninaccurate resistance determination and unnecessary rejection of thejumper cable.

Consequently, a need still exists for a grounding jumper cable testingdevice and testing method that avoids the problem of inductanceassociated with alternating current and provides a sufficient voltagedrop to break down any aluminum oxide coating on the clamps of thecable.

SUMMARY OF THE INVENTION

The present invention provides a protective grounding cable tester andtesting method designed to satisfy the aforementioned needs by avoidingthe drawbacks of the prior art without introducing other drawbacks.Accordingly, the present invention is directed to a protective groundingjumper cable tester and testing method for determining whether agrounding jumper cable has an adequately low resistance to current flowso that it may be safely used in a jumper system.

The protective grounding jumper cable tester of the present inventionbasically includes: (a) a housing, which may be portable for field useof the tester; (b) a pair of jumper attachment terminals on the housing;(c) a pair of test probe terminals on the housing; (d) a currentapplying circuit disposed in the housing and connected to the pair ofjumper attachment terminals for applying a direct current through ajumper cable attached between the jumper attachment terminals; and (f) aresistance sensing circuit disposed in the housing and connected to thetest probe terminals for sensing resistance to the flow of the directcurrent through the jumper cable by using a pair of test probesconnected to the test probe terminals. Further, the tester includes apower supply disposed in the housing and connected to the currentapplying circuit for producing the direct current flow therein andthrough the jumper cable.

One feature of the protective grounding jumper cable tester of thepresent invention is that it relies on direct current rather thanalternating current for testing the resistance of a grounding jumpercable to current flow. This avoids the problem of inductance associatedwith alternating current making irrelevant the positioning the jumpercable during testing.

Another feature of the protective grounding jumper cable tester of thepresent invention is that it more accurately determines the resistanceof a jumper cable having aluminum clamps. The thin aluminum oxidecoating that forms on the outside of aluminum clamps is highly resistantto current flow, but the direct current power supply of the testerprovides a sufficient voltage drop to break down the thin aluminum oxidecoating that forms on the outside of the aluminum clamps so that it doesnot affect the resistance of the jumper cable during testing.

The protective grounding jumper cable testing method of the presentinvention begins with connecting a jumper cable to be tested between apair of jumper attachment terminals and applying a direct current to thejumper attachment terminals so that a direct current flows through thejumper cable. Next, a meter connected across the terminals for sensingand indicating the quantity of the direct current flowing through thejumper cable is observed while the direct current flowing through thejumper cable is adjusted. If the direct current cannot be adjusted to afirst preselected quantity, then the jumper cable is either retestedafter being inspected and maintained (that is, cleaned and tightened orre-crimped) or it is rejected. If the direct current can be adjusted tothe first preselected quantity, then testing of the cable is continuedas set forth below. A resistance sensing meter is set to senseresistance within a first preselected test range and the jumperattachment terminals are contacted by a pair of test probes connected tothe resistance sensing meter so as to sense and indicate on theresistance sensing meter the resistance to the flow of the directcurrent through the jumper cable. The resistance indicated by theresistance sensing meter is compared with the first preselected testrange and the jumper cable is either accepted, retested after beinginspected and maintained, or rejected. The jumper cable is accepted ifthe indicated resistance is below a predetermined safe resistance level.If the resistance exceeds a predetermined safe level, the jumper cableis inspected, maintained and retested. If, during retesting, theresistance exceeds a predetermined safe level again, then the cable isrejected.

In the event that the resistance indicated by the resistance sensingmeter is below the preselected test range, the method further comprisesthe additional steps of applying second and third preselected directcurrents through the jumper cable that are greater than the firstpreselected direct current and setting the resistance sensing meter tosense resistances within second and third preselected test ranges whichare progressively lower than the first preselected test range. Theresistance of the jumper cable to the higher direct currents isindicated and compared successively with the respective second and thirdpreselected test ranges, with such comparisons resulting in the cableeither being accepted, retested or rejected as before.

One feature of the testing method of the present invention is that itinvolves the application of a direct current through the jumper cablebeing tested rather than an alternating test current. This avoids theproblem of inductance and eliminates the need for an additional step tominimize the possible effect of inductance during testing.

Another feature of the testing method of the present invention is theutilization of multiple preselected test ranges of resistance. Thisfeature increases the reliability and accuracy of the testing method.

These and other features and advantages of the present invention willbecome apparent to those skilled in the art upon a reading of thefollowing detailed description when taken in conjunction with thedrawings wherein there is shown and described an illustrative embodimentof the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following detailed description, reference will be made to theattached drawings in which:

FIG. 1 is a top plan view of a protective grounding jumper cable testerof the present invention.

FIG. 2 is a front elevational view of the tester.

FIG. 3 is schematic diagram of a current applying circuit of the tester.

FIG. 4 is a schematic diagram of a resistance sensing circuit of thetester.

FIG. 5 is an exploded side elevational view of a removable post and aconnection block of a jumper attachment terminal of the tester.

FIG. 6 is a perspective view of a protective grounding jumper cable thatmay be tested according to the testing method of the present invention.

FIG. 7 is a schematic diagram of the electrical equivalent circuit ofthe jumper cable of FIG. 6.

FIG. 8 is a flow chart showing the steps of an Initial Testing Start-Upprocedure of the protective grounding jumper cable testing method of thepresent invention.

FIG. 9 is a flow chart showing the steps of a Level Three Testingprocedure of the testing method.

FIG. 10 is a flow chart showing the steps of a Level Two Testingprocedure of the testing method.

FIG. 11 is a flow chart showing the steps of a Level One Testingprocedure of the testing method.

FIG. 12 is a flow chart showing the steps of an Inspect And Clean, thenDiscard or Retest procedure of the testing method.

FIG. 13 is a flow chart showing the steps of a Comparison With SafeResistance Value procedure of the testing method.

DETAILED DESCRIPTION OF THE INVENTION

Referring to the drawings, and particularly to FIGS. 1-4, there isillustrated a protective grounding jumper cable tester of the presentinvention, being generally designated 10. The tester 10 includes ahousing 12 which preferably, although not necessarily, is portable forreadily accommodating field use of the tester. The tester 10 also has acover 14 attached to the housing 12 by a pair of hinges 16 for pivotallyclosing the cover 14 during periods of non-use and opening the cover 14to gain access to the components therein, which are described below, forusing the tester 10.

The tester 10 also includes a power supply (PS) 18 which is disposedwithin the housing 12 below the top panel 12A thereof. The power supply18 receives alternating current and converts it into direct current.Mounted on the top panel 12A of its housing 12, the tester 10 furtherhas a power receptacle 20 adapted to receive a plug 22 of a power cord(not shown) to connect the power supply 18 to a source of thealternating current, such as a conventional sixty-cycle utility powerreceptacle, a power switch 24 operable for turning the tester 10 on andoff, a fuse 26 for protecting the circuitry of the tester 10, and anindicator light 28 which is lit when the tester 10 is on. Also, a fan(F) 30 is disposed within the housing 12 to help circulate air withinthe housing 12 and dissipate heat generated by the power supply 18 andthe other components of the tester 10. The power supply 18, powerreceptacle 20, switch 24, fuse 26, indicator light 28 and fan 30 areinterconnected as shown in the circuit diagram of FIG. 3. When thetester 10 is switched "on" by actuation of the power switch 24, thedirect current (d.c.) power supply 18 preferably supplies an output offive volts and up to twenty-five amps of direct current to the variouscomponents of the tester 10 described above and to the various circuitsof the tester 10 described below.

The tester 10 further includes a pair of jumper attachment terminals 32mounted at the front corners of the housing 12 for attachmenttherebetween of a jumper cable JC (see FIG. 6) to be tested and a pairof test probe terminals 34 spaced between and rearwardly of the jumperattachment terminals 32 for connection of a pair of test probes 36 (seeFIG. 4) thereto. As shown in greater detail in FIG. 5, each of thejumper attachment terminals 32 preferably includes an internallythreaded connection block 32A mounted in any suitable manner in one ofthe front corners of the housing 12 and an externally threaded removableterminal clamp attachment extension post 32B which threads into and fromthe connection block 32A to respectively deploy the post 32B for use andremove the post 32B for storage in the housing. Posts 32B havingdifferent sizes and shapes may be provided for facilitating theattachment of jumper cables JC having clamps CL of different sizes andshapes.

Referring now to FIGS. 1 and 3, the tester 10 also includes a currentapplying circuit 38 disposed in the housing 12 and connected between thed.c. power supply 18 and the pair of jumper attachment terminals 32 forapplying a direct current through the jumper cable JC attached betweenthe jumper attachment terminals 32, as shown in FIG. 6. The currentapplying circuit 38 preferably includes a current sensing meter (CM) 40connected in parallel with a current limiting resistor 42 and a variableresistor or rheostat 44 connected in series with each of them betweenthe d.c. power supply 18 and one of the jumper attachment terminals 32.The current sensing meter 40 indicates on a readout or display 40Athereof mounted on the top panel 12A of the housing 12 the quantity ofdirect current applied through the jumper cable JC by the currentapplying circuit 38. By turning a knob 44A on the rheostat 44 disposedabove the top panel 12A of the housing 12, the rheostat 44 is used toadjust the direct current applied through the jumper cable JC by thecurrent applying circuit 38 to a preselected quantity, such as fiveamps.

Referring now to FIGS. 1 and 4, the tester 10 further includes aresistance sensing circuit 46 disposed in the housing 12 and connectedto the pair of test probe terminals 34 for sensing resistance of thejumper cable JC to the flow of the direct current applied therethroughby the current applying circuit 38. Preferably, the resistance sensingcircuit 46 includes a resistance measuring meter (RM) 48 having areadout or display 48A mounted on the top panel 12A of the housing 12which provides resistance readings in milliohms and a resistancemeasuring meter range selector switch 50 having a rotatable knob 50Adisposed above the top panel 12A for turning to select a desired one ofa plurality of predetermined resistance test ranges, for example, 1 to20 milliohms, 20 to 200 milliohms and 200 to 900 milliohms. The pair oftest probes 36 are connected to the test probe terminals 34. When thepositive and negative test probes 36 are brought into contact with therespective positive and negative jumper attachment terminals 32, theresistance of the jumper cable JC to the flow of the direct currentapplied therethrough by the current applying circuit 38 is measured bythe resistance measuring meter 48 and indicated on the resistance meterdisplay 48A on the top panel 12A of the housing 12. The resistance rangeselector switch 44 may be used to select a particular one of thepredetermined resistance test ranges so that the resistance measuringmeter 48 may more accurately measure the resistance of the jumper cableJC. The resistance sensing circuit 46 also includes scaling resistors 52which allow the resistance measuring meter 48 to be interpreted directlyin milliohms of resistance instead of volts. The rotary resistance rangeselector switch 50 provides the full scale ranges of resistance that canbe read. The contact arm 50B has three different portions showndiagrammatically and identified as A, B and C in FIG. 4 which arerotated by rotation of the knob 50A of the switch 50 also shown in FIG.4. The portions of the contact arm 50B and knob 50A can be rotatedbetween four possible positions labeled as 1, 2, 3 and 4 in FIG. 4. Thepositions of the portion A of the contact arm 50B determines thelocation of the decimal point (D2, D3) on the display 48A of theresistance measuring meter 48. The portion B of the contact arm 50B isassociated with the resistance sensing circuit 46 and its variouspositions change the scaling of the resistance measuring meter 48. Allof the positions of the portion C of the contact arm 50B provides directcurrent voltage from the power supply 18 to the various components ofthe tester 10.

The preferred jumper cable testing method of the present invention isillustrated by the flow charts 54, 56, 58, 60, 62 and 64 of FIGS. 8through 13, respectively. The testing method is most effectivelyperformed by utilizing the tester 10 of the present invention. Moreparticularly, the flow chart 54 of FIG. 8 shows the steps of an InitialTesting Start-up procedure of the testing method. The flow chart 56 ofFIG. 9 illustrates the steps of a Level Three Testing procedure of thetesting method. The flow chart 58 of FIG. 10 depicts the steps of aLevel Two Testing procedure of the testing method. The flow chart 60 ofFIG. 11 shows the steps of a Level One Testing procedure of the testingmethod. The flow chart 62 of FIG. 12 depicts the steps of an Inspect andClean, then Discard or Retest procedure of the testing method. Finally,the flow chart 64 of FIG. 13 depicts the steps of a Comparison With SafeResistance Value procedure of the testing method.

Referring now to the flow chart 54 of FIG. 8, the Initial TestingStart-Up procedure of the testing method begins, as per block 66, withsetting up the tester 10 and installing the terminal clamp attachmentextension posts 32B into the connection blocks 32A. Next, as per block68, the rheostat 44 is adjusted to zero so that the current applyingcircuit 38 applies minimal current when the tester 10 is switched on.Then, as per block 70, the jumper cable JC that is to be tested isconnected between the posts 32B of the jumper attachment terminals 32,as shown in FIG. 6, and after doing so, as per block 72, the tester 10is switched on to apply a direct current through the jumper cable JC.

Referring next to the flow chart 56 of FIG. 9, once the above-describedinitial steps are completed, the testing method continues with LevelThree Testing procedure as indicated at the end of the flow chart 54 ofFIG. 8. As per block 74, the resistance measuring meter range selectorswitch 50 is set to a first preselected test range, for example, byrotating the knob 50A to position 4 identified as 200-900 milliohms.Next, as per block 76, the direct current flowing through the jumpercable JC is adjusted while observing the current sensing meter 40. Thedirect current is adjusted by turning the rheostat knob 44A until thedirect current indicated on the current sensing meter display 40Areaches a first preselected quantity, for example 5 amps. As per diamond78, if the direct current cannot be adjusted to reach the firstpreselected quantity (the answer to the question in the diamond 78 isNo), then the jumper cable JC is either retested after being inspectedand maintained or it is rejected according to the steps shown in theflow chart 62 of FIG. 12 which are described below. Level three testingcontinues only if the current can be adjusted to the first preselectedquantity (the answer to the question in the diamond 78 is Yes). If so,as per block 80, the test probes 36 are brought into contact with theposts 32B to sense and indicate the resistance of the jumper cable JC tothe flow of the direct current therethrough on the resistance meterdisplay 48A. As per block 82, the amount of resistance is read from thedisplay 48A. As per diamond 84, this resistance reading is compared withthe first preselected test range and, if it is within the firstpreselected test range (the answer to the question is diamond 84 isBetween), then the jumper cable JC is either accepted, retested, orrejected in accordance with the steps shown in the flow chart 64 of FIG.13 which are described below. If the indicated resistance is below thefirst preselected test range (the answer to the question in diamond 84is Below), then it is necessary to proceed with the steps for level twotesting as shown in the flow chart 58 of FIG. 10 which are describedbelow.

Referring next to the flow chart 58 of FIG. 10, the Level Two Testingprocedure of the testing method begins, as per block 86, with settingthe resistance measuring meter range selector switch 50 to a secondpreselected test range which is below the first preselected test range,for example, by rotating the knob 50A to position 3 identified as 20-200milliohms. The current is then adjusted, as per block 88, by furtherturning the rheostat knob 44A until it reaches a second preselectedquantity which is greater than the first preselected quantity, forexample, 10 amps. Once the current is adjusted to the second preselectedquantity, as per block 90, the test probes 36 are brought into contactwith the posts 32B to indicate the resistance of the jumper cable JC onthe resistance meter display 48A. As per block 92, the amount ofresistance is read from the display 48A. As per diamond 94, this secondresistance reading is compared with the second preselected test rangeand, if it is within the second preselected test range (the answer tothe question in diamond 94 is Between), then the jumper cable JC iseither accepted, retested, or rejected in accordance with the steps ofthe procedure shown in the flow chart 64 of FIG. 13 which are describedbelow. If the indicated resistance is below the second preselected testrange (the answer to the question in diamond 94 is Below), then it isnecessary to proceed with the steps for Level One Testing procedure asshown in the flow chart 60 of FIG. 11 which are described below.

Referring next to the flow chart 60 of FIG. 11, the Level One Testingprocedure of the testing method begins, as per block 96, with settingthe resistance measuring meter range selector switch 50 to a thirdpreselected test range which is below the second preselected test range,for example, by rotating the knob 50A to position 2 identified as 1-20milliohms. As per block 98, the current is then adjusted as before untilit reaches a third preselected quantity which is substantially equal tothe second preselected quantity, for example 10 amps. Once the currentis adjusted to the third preselected quantity, as per block 100, thetest probes 36 are brought into contact with the posts 32B to indicatethe resistance of the jumper cable JC on the resistance meter display48A. As per block 102, the amount of resistance is read from the display48A. As per diamond 104, this third resistance reading is compared withthe third preselected test range and, if it is within the thirdpreselected test range (the answer to the question in diamond 104 isBetween), then the jumper cable JC is either accepted, retested, orrejected in accordance with the steps of the flow chart 64 of FIG. 13which are described below. If the indicated resistance is below thethird preselected test range (the answer to the question in diamond 104is Below), then testing of the jumper cable JC is completed and theresistance of the jumper cable is acceptable, as per block 106.

Referring now to FIG. 12, when the direct current through the jumpercable JC cannot be adjusted to the first preselected quantity during theLevel Three Testing procedure it is necessary to perform the Inspect &Clean, Discard or Retest procedure of flow chart 62. This procedureinvolves first inspecting and maintaining (that is, cleaned andtightened or re-crimped) the jumper cable JC, then retesting itaccording to the steps for the Level Three Testing procedure of the flowchart 56 of FIG. 9. Also, the steps shown in the flow chart 64 of FIG.13 and set forth below may also call for inspection and maintenance ofthe cable before retesting it at the current testing level. Accordingly,as per diamond 108 of flow chart 62, if the jumper cable JC has not yetbeen inspected and maintained (answer to the question in diamond 108 isNo), then the jumper cable is inspected for conditions which mightaffect its resistance, such as faulty connections, broken wires orexcessively corroded clamps, and maintenance is performed to the jumpercable JC to remedy any such conditions, as per block 110. Once inspectedand maintained, the jumper cable JC is retested according to the stepsof the appropriate testing level. However, if the jumper cable JC hasalready been inspected and maintained (answer to the question in diamond108 is Yes) and it is presently being retested then there is no need forfurther inspection and maintenance and the cable is rejected, as perblock 112.

Referring finally to FIG. 13, when the indicated resistance of thejumper cable JC to the flow of the applied direct current therethroughis within either the first, second or third preselected test ranges, itis then necessary to compare the indicated resistance with apredetermined safe resistance value according to the Comparison WithSafe Resistance Value procedure of flow chart 64. After the comparisonis performed, as per block 114, if the indicated resistance is below thepredetermined safe resistance value (the answer to the question indiamond 116 is Yes), then testing is completed and the jumper cable JCis accepted, as per block 118. If the indicated resistance exceeds thepredetermined safe resistance value (the answer to the question indiamond 116 is No), then it may be necessary to test the jumper cable JCto locate the points of high resistance, as per block 120, by performinginspection and maintenance on the jumper cable JC and then retest it inaccordance with the steps of the flow chart 62 of FIG. 12 which aredescribed above.

Thus, before performing inspection of the cable in accordance with thesteps of the flow chart 62 of FIG. 12, it is preferable to locate theportions of the jumper cable JC which are contributing to a highresistance reading. This may be accomplished by using the test probes 36to make resistance readings of various portions of the jumper cable JC.As shown in FIG. 6, a typical jumper cable JC consists of a pair ofclamps CL and a cable CA which extends between and interconnects theclamps CL. The cable CA is attached at either end to the clamps CL by aferrule FL. When the jumper cable JC is attached between the jumperattachment terminals 32, it completes the current applying circuit 38and may be represented by the electrical equivalent circuit shown inFIG. 7. The total resistance of the jumper cable JC is comprised of aplurality of lesser resistances: the resistance R1 of the surfacecontact between one clamp CL and the jumper attachment terminal 32; theresistance R2 of the clamp CL itself; the resistance R3 of the ferruleFL; the resistance R4 of the cable CL; the resistance R5 of the otherferrule FL; the resistance R6 of the other clamp CL; and the resistanceR7 of the surface contact between the other clamp CL and the otherjumper attachment terminal 32. The resistance R1 and R7 of the surfacecontacts between the clamps CL and the jumper attachment terminals 32may be determined by contacting the test probes 36 at the test pointsTP1 and TP7 in FIGS. 6 and 7. This may indicate whether excessivecorrosion on the surface of the clamps CL is adversely affecting theresistance of the jumper cable JC. The resistances R2 and R6 of theclamps CL may be determined by contacting the test probes 36 at the testpoints TP2 and TP6 in FIGS. 6 and 7. This may indicate whether theclamps CL are adversely affecting the resistance of the jumper cable JC.The resistances R3 and R5 of the ferrules FL may be determined bycontacting the test probes 36 at the test points TP3 and TP5 in FIGS. 6and 7. This may indicate whether the ferrules FL are adversely affectingthe resistance of the jumper cable JC. Finally, the resistance R4 of thecable CA may be determined by contacting the test probes at the testpoints TP4 in FIGS. 6 and 7. This may indicate whether the cable CA isadversely affecting the resistance of the jumper cable JC. Once theportions of the jumper cable JC that are adversely affecting itsresistance are identified, special attention may be paid to theseportions during inspection and maintenance.

It is thought that the present invention and its advantages will beunderstood from the foregoing description and it will be apparent thatvarious changes may be made thereto without departing from the spiritand scope of the invention or sacrificing all of its materialadvantages, the form hereinbefore described being merely preferred orexemplary embodiment thereof.

I claim:
 1. A protective grounding jumper cable tester, comprising:(a) ahousing having a top panel extending thereacross; (b) a pair of jumperattachment terminals mounted on said top panel of said housing forattachment of a jumper cable therebetween, said jumper attachmentterminals including a base member fixedly attached on said housing and apost member having means releasably engageable with complementaryengaging means on said base member for temporary attachment of said postmember to said base member such that said post member extends outwardlyfrom said top panel of said housing; (c) a pair of test probe terminalsmounted on said top panel of said housing for connection of a pair oftest probes thereto; (d) a current applying circuit disposed in saidhousing below said top panel and connected to said pair of jumperattachment terminals for applying a direct current through a jumpercable attached between said jumper attachment terminals; and (e) aresistance sensing circuit disposed in said housing below said top paneland connected to said pair of test probe terminals for sensingresistance of the jumper cable attached between said jumper terminals tothe flow of said direct current therethrough by using a pair of testprobes connected to said test probe terminals.
 2. The tester of claim 1,wherein said current applying circuit includes:a current sensing metermounted on said top panel for sensing said direct current appliedthrough the jumper cable and to display the quantity of direct currentapplied through the jumper cable; and a rheostat for adjusting saiddirect current applied through the jumper cable until a preselectedquantity is indicated by said current measuring meter, said rheostathaving a turning knob disposed above said top panel of said housingoperable for adjusting the direct current applied through the jumpercable by turning of said knob.
 3. The tester of claim 1, wherein saidresistance sensing circuit includes:a resistance measuring meter forindicating the resistance of the jumper cable to the flow of said directcurrent therethrough, said resistance measuring meter having a displaymounted on said top panel of said housing which provides resistancereadings in milliohms; and a resistance measuring meter range selectorswitch having a rotatable knob disposed above said top panel of saidhousing for selecting at least one predetermined resistance test rangewithin which said resistance measuring meter indicates the resistance ofthe jumper cable to the flow of said direct current therethrough.
 4. Thetester of claim 3, wherein said resistance measuring meter rangeselector switch is operable for selecting one of a plurality ofdifferent predetermined resistance test ranges.
 5. The tester of claim1, wherein said base member of said jumper attachment terminal is aninternally threaded connection block and said post member of said jumperattachment terminal is externally threaded so as to thread into and fromsaid connection block to respectively deploy said post member for useand remove said post member for storage in said housing.
 6. A protectivegrounding jumper cable tester, comprising:(a) a housing having a toppanel extending thereacross; (b) a power supply disposed within saidhousing below said top panel for receiving alternating current andproducing a direct current output; (c) a pair of jumper attachmentterminals mounted on said top panel of said housing for attachment of ajumper cable therebetween, said jumper attachment terminals including abase member fixedly attached on said housing and a post member havingmeans releasably engageable with complementary engaging means on saidbase member for temporary attachment of said post member to said basemember such that said post member extends outwardly from said top panelof said housing; (d) a pair of test probe terminals mounted on said toppanel of said housing for connection of a pair of test probes thereto;(e) a current applying circuit in said housing connected between saidpower supply and said pair of jumper attachment terminals for applying adirect current through a jumper cable attached between said jumperattachment terminals, said current applying circuit including:(i) acurrent sensing meter mounted on said top panel for sensing said directcurrent applied through the jumper cable and to display the quantity ofdirect current applied through the jumper cable; and (ii) a rheostat foradjusting said direct current applied through the jumper cable until apreselected quantity is indicated by said current measuring meter, saidrheostat having a turning knob disposed above said top panel of saidhousing operable for adjusting the direct current applied through thejumper cable by turning of said knob; and (f) a resistance sensingcircuit in said housing connected to said pair of test probe terminalsfor sensing resistance of the jumper cable to the flow of said directcurrent therethrough by using a pair of test probes connected to saidtest probe terminals, said resistance sensing circuit including:(i) aresistance measuring meter for indicating the resistance of the jumpercable to the flow of said direct current therethrough, said resistancemeasuring meter having a display mounted on said top panel of saidhousing which provides resistance readings in milliohms; and (ii) aresistance measuring meter range selector switch having a rotatable knobdisposed above said top panel of said housing for selecting at least onepredetermined resistance test range within which said resistancemeasuring meter indicates the resistance of the jumper cable to the flowof said direct current therethrough.
 7. The tester of claim 6, whereinsaid resistance measuring meter range selector switch is operable forselecting one of a plurality of different predetermined resistance testranges.